Traditionally, the timing between the camshaft and crankshaft are fixed for some predetermined optimum engine speed, but the timing will then be less than optimum at other engine speeds. Varying the timing between the camshaft and crankshaft by accurately modulating the phase shift, to ensure that it is optimized during engine operation, produces several benefits. It is common knowledge that adequate phase shifting will improve idle stability, the broadness of the torque curve and the RPM (revolutions per minutes) range of the engine. Additional benefits to be expected are (i) full control of emission gases and elimination of undesirable emissions [NOx], (ii) part load fuel efficiency improvements and (iii) elimination of external exhaust gas recirculation components and circuitry [EGR].
In developing a device to obtain these benefits, several important considerations are taken into account. The control system of the device should require low power consumption. Further, the response of the system must be fast and accurate to maximize these benefits. Also, a system must be capable of being modulated incrementally throughout an entire range, as opposed to two position phase shifting, i.e., full advance or full retard only, to improve the overall effectiveness of the device.
Prior art, such as U.S. Pat. Nos. 3,685,499 and 3,721,220, have incorporated hydraulic means to accomplish phase shifts between the camshaft and crankshaft to achieve some of these benefits.
In U.S. Pat. No. 3,685,499, to Meacham et al, the phase shifting device is a helical ball spline mechanism. A driven member is fixed to the camshaft and connected by a helical ball spline to a piston which is rotatably fixed relative to the crankshaft. The inner and outer races of the ball spline form an enclosed cavity for hydraulic fluid. This is not a closed system since the flow of fluid into or out of the cavity, to obtain the phase shift, comes from outside the system, i.e. the primary engine oil source, and is continuous throughout the phase shift. Further, it requires the engine oil pressure as the source of energy for effecting the phase shift.
In U.S. Pat. No. 3,721,220 to Garcea, this is shown in a phase shifting device consisting of a drive and driven flange with a pair of hydraulic cylinders which rotate the flanges relative to one another. These cylinders, however, are much different than the present invention. The cylinders are not interconnected and both work in parallel, to accomplish a phase shift, when shifted outward by engine oil pressure.